WALNUT HUSK FLY (DIPTERA, TEPHRITIDAE) PEST-FREE AND PREOVIPOSITIONALPERIODS AND ADULT EMERGENCE FOR STONE FRUITS EXPORTED TO NEW-ZEALAND

Walnut husk fly, Rhagoletis completa Cresson, adults were trapped in t wo of nine trap locations in walnuts in five counties in the San joaqu in Valley of California before the end of the pest-free period, 1 July 1992. Highest numbers of adults were collected in walnuts from 19 Aug ust through 8 October after early-season, midseason, and most late-sea son stone fruit cultivars had been harvested. Lowest numbers of adults were trapped in Kern County locations in the southern region of the S an joaquin Valley. Laboratory behavioral studies showed that earliest ovipositional punctures in walnuts occurred 9 d after and eggs were la id 11 d after adult emergence. The preovipositional period will reduce the risk of stone, fruit infestations during atypical years when adul ts emerge before 1 July. Adults emerged from pupae reared in the previ ous year from peaches, nectarines, and walnuts, but no adults emerged from plums. The biological risk for accidental introductions of walnut husk fly into New Zealand through shipments of stone fruits from Cali fornia is negligible.